Low-temperature low-sulfur synthesis gas purification process matched with coal water slurry gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature low-sulfur synthesis gas purification method and device matched with a coal water slurry gasification device.According to the method, the H2S absorption process is optimally set, low-sulfur carbon-rich methanol and low-H2S methanol are used for washing synthesis gas, and the use amount of CO2-rich methanol is reduced; the technical problem that CO2 gas is polluted by H2S gas in the medium-pressure flash evaporation process is solved by optimally setting the medium-pressure flash evaporation process and using classified flash evaporation and classified washing technologies; by optimizing the flow of the re-absorption tower, low-H2S methanol is generated and is prevented from being deeply polluted at the same time, and the low-temperature methanol washing device has the characteristic of low comprehensive energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature methanol washing, and specifically relates to a method for purifying low-temperature and low-sulfur synthesis gas for a coal water slurry gasification device and a device for purifying low-temperature and low-sulfur synthesis gas for a coal water slurry gasification device. Background Art

[0002] In the synthesis gas produced by using the coal water slurry gasification technology, H 2 and CO are called effective gases. At the same time, the synthesis gas also contains a large amount of CO 2 and trace amounts of H 2 S, COS, NH 3 , HCN and other components. Among them, H 2 and CO are the raw material gases for synthesizing chemical products such as methanol, ammonia, and ethylene glycol after adjusting the hydrogen-carbon ratio through the shift unit. The acidic gases CO 2 and H 2 S in the synthesis gas are generally poisons for synthesis catalysts, so they must be removed before the synthesis process.

[0003] The low-temperature methanol washing technology uses low-temperature methanol as the absorption solvent, and utilizes the characteristic that low-temperature methanol has a great solubility for acidic gases to remove H 2 S and CO 2 and other acidic gases in the synthesis gas, and at the same time removes trace components such as HCN and NH 3 . At present, the innovative research on the low-temperature methanol washing technology mainly focuses on the recycling of the pressure-reducing flash evaporation of rich CO 2 methanol. The typical process flow mainly includes the lean liquid-semi-lean liquid process, but there are technical bottlenecks in further optimizing and innovating the lean liquid-semi-lean liquid process. Therefore, it is necessary to appropriately adjust the technical innovation direction of the low-temperature methanol washing process.

[0004] In the low-temperature methanol washing process flow, the rich CO 2 methanol can be recycled through pressure-reducing flash evaporation, but the H 2 S-containing methanol must be recycled through thermal regeneration, which is the main energy-consuming source of low-temperature methanol washing. Therefore, how to enhance the use efficiency of H 2 S-containing methanol is the key factor in technological innovation.

[0005] CN201110260570.0 discloses a low-temperature methanol washing process. First, in the H 2 S absorption tower, all rich CO 2 methanol is used to wash the synthesis gas, which increases the usage amount of rich CO 2 methanol. The generated rich H 2 S methanol needs to be thermally regenerated before it can be recycled, resulting in high energy consumption. Second, in the CO 2 flash evaporation section of the reabsorption tower, rich CO2 Methanol is used to wash the rich H 2 S methanol flash vapor while directly mixing with the rich H 2 S methanol, and itself is contaminated by the rich H 2 S methanol, and the resulting low-concentration H 2 S methanol is sent to the post-system regeneration without being fully utilized, resulting in high energy consumption; thirdly, the CO 2 gas flashed out from the upper tower of the medium-pressure flash tower is contaminated while being washed by the rich H 2 S methanol, which is not conducive to reducing the comprehensive energy consumption of the cold methanol washing unit. Summary of the Invention

[0006] In order to overcome the above technical problems, the present invention provides a method for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit and a device for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit. By optimizing the H 2 S absorption process, using low-sulfur and carbon-rich methanol and low-H 2 S methanol to wash the syngas, the usage amount of rich CO 2 methanol is reduced; by optimizing the medium-pressure flash process and using the classified flash and classified washing technologies, the technical problem of the CO 2 gas being contaminated by the H 2 S gas in the medium-pressure flash process is solved; by optimizing the reabsorption tower process, low-H 2 S methanol is generated, and at the same time, the deep contamination of low-H 2 S methanol is avoided, and the cold methanol washing unit has the characteristic of low comprehensive energy consumption.

[0007] To achieve the above object, the first aspect of the present invention provides a method for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit, the method comprising:

[0008] Performing H 2 S absorption on the syngas to obtain first rich H 2 S methanol and desulfurized gas; performing CO 2 absorption on the desulfurized gas, and dividing the obtained rich CO 2 methanol into two streams; cooling the second stream of rich CO 2 methanol for the first time and then performing CO 2 flash to obtain the flashed rich CO 2 methanol divided into two streams, the first stream of the flashed rich CO 2 methanol is subjected to the first flash to obtain semi-lean liquid methanol divided into two streams, and the second stream of the flashed rich CO 2 methanol is cooled for the second time and then subjected to the second flash; performing H 2 S flash on the first rich H 2 S methanol to obtain the flashed rich H 2The methanol containing sulfur is subjected to a third flash evaporation after the third cooling, and the sulfur-containing gas phase obtained is subjected to a first washing with the flashed solution obtained from the second flash evaporation to obtain low-H 2 methanol containing sulfur;

[0009] Among them, the first semi-lean methanol is divided into three streams. The A-stream semi-lean methanol is returned and subjected to the above-mentioned CO 2 absorption. The B-stream semi-lean methanol is subjected to a second washing with the CO 2 flashed gas obtained from the CO 2 flash evaporation. The C-stream semi-lean methanol is subjected to a third washing with the H 2 flashed gas obtained from the H 2 S flash evaporation to obtain low-sulfur carbon-rich methanol;

[0010] Among them, the low-H 2 methanol containing sulfur, the first rich-CO 2 methanol, and the low-sulfur carbon-rich methanol are each independently returned and subjected to the above-mentioned H 2 S absorption.

[0011] The second aspect of the present invention provides a low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device. The device includes: an H 2 S absorption tower, a CO 2 absorption tower, a medium-pressure flash evaporation tower, and a reabsorption tower, which are connected in sequence, and a first cooler, a second cooler, and a third cooler; the medium-pressure flash evaporation tower includes a CO 2 flash evaporation section provided on the upper part and an H 2 S flash evaporation section provided on the lower part, and the H 2 S flash evaporation section is divided into an upper section and a lower section;

[0012] The syngas enters the H 2 S absorption tower for H 2 S absorption to obtain the first rich-H 2 methanol containing sulfur and desulfurized gas; the desulfurized gas enters the CO 2 absorption tower for CO 2 absorption to obtain the rich-CO 2 methanol, which is divided into two streams. The first rich-CO 2 methanol is recycled and used in the H 2 S absorption tower. The second rich-CO 2 methanol enters the CO 2 flash evaporation section after passing through the first cooler for CO 2 flash evaporation to obtain the flashed rich-CO 2 methanol, which is divided into two streams. The first flashed rich-CO 2 methanol enters the upper part of the reabsorption tower for the first flash evaporation to obtain the semi-lean methanol, which is divided into two streams. The second flashed rich-CO 2 methanol enters the middle part of the reabsorption tower for the second flash evaporation after passing through the second cooler;

[0013] Feed the first H-rich 2 S methanol into the 2 lower part of the H 2 S flash section for 2 H flash. After flash, the H-rich 2 S methanol enters the lower part of the reabsorption column after passing through the third cooler for the third flash. The sulfur-containing gas phase obtained and the solution after the second flash are subjected to the first washing, and the low-H 2 S methanol is recycled to the

[0014] Among them, the first semi-lean methanol is divided into three streams. The A-stream semi-lean methanol is recycled to the CO 2 absorption column, the B-stream semi-lean methanol is recycled to the CO 2 flash section for the second washing, and the C-stream semi-lean methanol is recycled to the 2 upper part of the H 2 S flash section for the third washing. The low-sulfur carbon-rich methanol obtained is recycled to the

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) In the method provided by the present invention, by optimizing the medium-pressure flash process, the B-stream semi-lean methanol is used to wash the CO 2 flash gas flashed from the second CO-rich 2 methanol. Compared with the prior art, while reducing the CO 2 component in the CO flash gas, it is not contaminated by the H-rich 2 S methanol; at the same time, the C-stream semi-lean methanol is used to wash the H 2 S flash gas flashed from the first H-rich 2 S methanol. Compared with the prior art, while reducing the CO 2 component in the H 2 S flash gas, the washing liquid is not deeply contaminated by the H-rich 2 S methanol after flash; the separate flashing and separate washing of the second CO-rich 2 methanol and the first H-rich 2 S methanol are realized, avoiding the technical problem that the CO 2 gas in the CO-rich methanol after flash is transferred to the H-rich 2 S methanol after flash. At the same time, the low-sulfur carbon-rich methanol after the third washing is reused, which is beneficial to reducing the energy consumption of the device; 2 2 2 (2) In the method provided by the present invention, for CO

[0017] ​​The reabsorption process flow is optimized to achieve the rich CO after the second flash 2 The flash liquid of methanol, and the sulfur-containing gas phase of the rich H 2 S methanol flash is subjected to the first washing, so that the H 2 S content in the solution is lower, and low H 2 S methanol is obtained; at the same time, the flash liquid of the second rich CO 2 Methanol does not mix with the rich H 2 S methanol after flashing;

[0018] (3) The method provided by the present invention, by introducing low H 2 S methanol and low-sulfur rich-carbon methanol jointly absorb H 2 S and CO 2 Gas in the syngas, realizing the recycling of low H 2 S methanol and low-sulfur rich-carbon methanol, reducing the H 2 Usage amount of the first rich CO 2 Methanol is equivalent to reducing the rich H 2 S methanol that needs to be thermally regenerated; in addition, during the H 2 S absorption process, through the joint absorption of CO 2 By low H 2 S methanol and low-sulfur rich-carbon methanol, the working load of the subsequent CO 2 Absorption tower is correspondingly reduced, and the usage amounts of lean methanol and semi-lean liquid methanol during the CO 2 Absorption process are also appropriately reduced. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of a low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device provided by the present invention.

[0020] Description of the Reference Numerals

[0021] T-1, H 2 S absorption tower; T-2, CO 2 Absorption tower; T-3, medium-pressure flash tower; T-4, reabsorption tower; E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; E-5, fifth cooler; P-1, first pump; P-2, second pump; P-3, third pump; P-4, fourth pump; 1, syngas; 2, low H 2 S methanol; 2-i, the first low H 2 S methanol; 2-ii, the second low H 2 S methanol; 3, the second rich H 2 S methanol; 4, the first rich H 2 S methanol; 5, desulfurized gas; 6, rich CO2 Methanol; 6-i, the first rich CO 2 Methanol; 6-ii, the second rich CO 2 Methanol; 7, CO-containing 2 Methanol; 8, semi-lean methanol; 8-i, the first semi-lean methanol; 8-ii, the second semi-lean methanol; 8-i-A, A-share semi-lean methanol; 8-i-B, B-share semi-lean methanol; 8-i-C, C-share semi-lean methanol; 9, lean methanol; 10, purified gas; 11, low-sulfur rich-carbon methanol; 12, flash gas; 12-i, the first flash gas; 12-ii, the second flash gas; 13, rich CO after flashing 2 Methanol; 13-i, the first rich CO after flashing 2 Methanol; 13-ii, the second rich CO after flashing 2 Methanol; 14, rich H 2 S methanol; 15, CO 2 Product gas; 16, the third rich H 2 S methanol. Detailed implementation manners

[0022] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0023] In the present invention, without special circumstances, "first", "second", "third", "fourth" and "fifth" neither represent the order nor limit each material or step, but are only used to distinguish that these are not the same material or step. For example. The "first", "second", "third", "fourth" and "fifth" in "first cooling", "second cooling", "third cooling", "fourth cooling" and "fifth cooling" are only used to indicate that these are not the same cooling.

[0024] In the present invention, without special circumstances, the "top" of the container refers to the 0-10% height of the container from top to bottom; the "upper part" of the container refers to the 10-40% height of the container from top to bottom; the "middle part" of the container refers to the 40-60% height of the container from top to bottom; the "lower part" of the container refers to the 60-90% height of the container from top to bottom; the "bottom" of the container refers to the 90-100% height of the container from top to bottom.

[0025] The first aspect of the present invention provides a low-temperature and low-sulfur syngas purification method for a supporting coal water slurry gasification device, and the method includes:

[0026] Subject the syngas to H 2 S absorption to obtain a first H 2 -rich methanol and desulfurized gas; subject the desulfurized gas to CO 2 absorption to obtain a CO 2 -rich methanol which is divided into two streams; subject the second stream of CO 2 -rich methanol to CO 2 flash after the first cooling to obtain a flash-off CO 2 -rich methanol which is divided into two streams, the first stream of flash-off CO 2 -rich methanol is subjected to a first flash to obtain semi-lean methanol which is divided into two streams, and the second stream of flash-off CO 2 -rich methanol is subjected to a second flash after the second cooling; subject the first H 2 -rich methanol to H 2 S flash to obtain a flash-off H 2 -rich methanol which is subjected to a third flash after the third cooling, and the sulfur-containing gas phase obtained is subjected to a first washing with the flash-off solution obtained from the second flash to obtain a low-H 2 S methanol;

[0027] Among them, the first stream of semi-lean methanol is divided into three streams, the A-stream of semi-lean methanol is returned and subjected to the above-mentioned CO 2 absorption, the B-stream of semi-lean methanol and the CO 2 flash gas obtained from the flash are subjected to a second washing, and the C-stream of semi-lean methanol and the H 2 flash gas obtained from the H 2 S flash are subjected to a third washing to obtain a low-sulfur carbon-rich methanol; 2

[0028] Among them, the low-H 2 S methanol, the first stream of CO 2 -rich methanol and the low-sulfur carbon-rich methanol are each independently returned and subjected to the above-mentioned H 2 S absorption.

[0029] In some embodiments of the present invention, preferably, the low-H 2 S methanol is pressurized to 5.6 - 6 MPa(G) by the first booster and then returned and subjected to the above-mentioned H 2 S absorption.

[0030] In some embodiments of the present invention, preferably, in the direction of material flow, the first stream of CO 2 -rich methanol is successively pressurized to 5.6 - 6 MPa(G) by the second booster and cooled to -35 to -25 °C by the fourth cooler, and then returned and subjected to the above-mentioned H 2 S absorption.

[0031] In some embodiments of the present invention, preferably, after the first semi-lean methanol is pressurized to 5.6 - 5.8 MPa(G) by the third compressor, it is divided into the A semi-lean methanol, the B semi-lean methanol, and the C semi-lean methanol.

[0032] In some embodiments of the present invention, preferably, after the low-sulfur and carbon-rich methanol is pressurized to 5.6 - 6 MPa(G) by the fourth compressor, it is returned for the H 2 S absorption.

[0033] In some embodiments of the present invention, preferably, the process of the H 2 S absorption includes: contacting the syngas with the first low-H 2 S methanol for pre-washing to obtain the second H-rich 2 S methanol and the pre-washed syngas; sequentially contacting the pre-washed syngas with the second low-H 2 S methanol, the low-sulfur and carbon-rich methanol, and the first CO-rich 2 methanol for main washing to obtain the first H-rich 2 S methanol and the desulfurized gas;

[0034] wherein, the low-H 2 S methanol is divided into the first low-H 2 S methanol and the second low-H 2 S methanol with a molar flow rate ratio of 1:13 - 15.

[0035] In some embodiments of the present invention, preferably, the molar content of H 2 S in the syngas is 0.9 - 1.2%, and the molar content of CO 2 is 40 - 50%; the temperature is -15 to -5 °C, and the pressure is 5.2 - 5.7 MPa(G).

[0036] In the present invention, there is a relatively wide selection range for the source of the syngas, as long as the syngas meets the above limitations. Preferably, the syngas is selected from the upstream syngas cooling process.

[0037] In some embodiments of the present invention, preferably, the molar flow rate ratio of the first low-H 2 S methanol to the syngas is 1:70 - 80.

[0038] In the present invention, the purpose of the pre-washing is to remove impurities such as HCN and NH 3 in the syngas, as well as a small amount of H 2 S and CO 2 . Preferably, the molar content of H 2 S in the second H-rich 2 S methanol is 0.2 - 0.4%, and CO2 The molar content is 70 - 75%.

[0039] In some embodiments of the present invention, preferably, the second low-H 2 The molar flow ratio of S methanol to syngas is 1:5 - 6.

[0040] In some embodiments of the present invention, preferably, the molar flow ratio of low-sulfur carbon-rich methanol to syngas is 1:7 - 8.

[0041] In some embodiments of the present invention, preferably, the first CO-rich 2 The molar flow ratio of methanol to syngas is 1:2 - 3.

[0042] In the present invention, the main washing aims to further remove H 2 S, as well as a small amount of CO 2 . Preferably, the H 2 in the first H-rich 2 S methanol has a molar content of 1.2 - 1.4%, and CO 2 has a molar content of 38 - 42%; the temperature is -20 to -10 °C, and the pressure is 5.3 - 5.4 MPa(G).

[0043] In some embodiments of the present invention, preferably, the H 2 in the desulfurized gas has a molar content of 0.5 - 1 ppm, and CO 2 has a molar content of 36 - 40%; the temperature is -20 to -10 °C; the pressure is 5.3 - 5.4 MPa(G).

[0044] In the present invention, without special instructions, the CO-rich 2 methanol is divided into two streams. Preferably, the CO-rich 2 methanol is divided into a first CO-rich 2 methanol and a second CO-rich 2 methanol with a molar flow ratio of 1:2 - 2.3.

[0045] In some embodiments of the present invention, preferably, the process of CO 2 absorption includes: contacting the desulfurized gas with CO-containing 2 methanol and performing pre-purification to obtain pre-purified gas and the CO-rich 2 methanol; contacting the pre-purified gas, A-type semi-lean liquid methanol, and lean methanol and performing main purification to obtain the CO-containing 2 methanol and purified gas.

[0046] In the present invention, the pre-purification aims to further remove CO in the desulfurized gas 2. Preferably, the molar content of CO in the rich CO 2 in methanol is 30 - 34%, and the molar content of H 2 S is 0.1 - 0.5 ppm; the temperature is -15 to -10 °C, and the pressure is 5.2 - 5.4 MPa(G). 2 In some embodiments of the present invention, preferably, the molar flow ratio of the desulfurized gas to the CO

[0047] -containing methanol is 1:1.1 - 1.4. 2 In some embodiments of the present invention, more preferably, after the CO

[0048] -containing methanol is cooled to -36 to -34 °C by the fifth cooler, it is returned for the pre-absorption. 2 In some embodiments of the present invention, preferably, the molar flow ratio of the purified gas to the A-share semi-lean methanol is 1.4 - 1.6:1.

[0049] In some embodiments of the present invention, preferably, the molar flow ratio of the purified gas to the lean methanol is 1:1 - 1.2. In the present invention, the lean methanol comes from the subsequent process, and the molar content of H

[0050] S in the lean methanol is 0%, and the molar content of CO 2 is 0%. 2 In some embodiments of the present invention, preferably, the molar content of H

[0051] S in the purified gas is ≤0.1 ppm, and the molar content of CO 2 is ≤20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G). 2 In the present invention, the first cooling is achieved by reducing the temperature of the second stream of rich CO

[0052] -containing methanol, aiming to reduce the total amount of medium-pressure flash gas and lay a foundation for obtaining low temperature (high-quality cold energy) for the re-absorption tower. Preferably, the temperature of the material after the first cooling is -36 to -34 °C. 2 In the present invention, the process of CO

[0053] flashing includes: flashing the material after the first cooling to obtain CO 2 flashed gas and rich CO 2 -containing methanol after flashing. Preferably, the pressure of the CO 2 flashing is 1.6 - 2 MPa(G). 2 In some embodiments of the present invention, preferably, the rich CO 2 -containing methanol after flashing

[0054] after flashing is 2The methanol is divided into the first flash-rich CO methanol with a molar flow ratio of 3 - 3.6:1 and the second flash-rich CO methanol. 2 The methanol is divided into the first flash-rich CO methanol with a molar flow ratio of 3 - 3.6:1 and the second flash-rich CO methanol. 2 methanol.

[0055] In some embodiments of the present invention, preferably, the H₂S molar content in the flash-rich CO methanol is 0.1 - 0.5 ppm, the CO molar content is 29 - 33%; the temperature is -38 to -35 °C. 2 In the present invention, the flash-rich CO methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C. 2 S molar content is 0.1 - 0.5 ppm, and the CO molar content is 29 - 33%; the temperature is -38 to -35 °C. 2 the molar content of CO is 29 - 33%; the temperature is -38 to -35 °C.

[0056] In the present invention, the flash-rich CO methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C. 2 The methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C. 2 The methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C. 2 The methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C.

[0057] In the present invention, the process of the first flash includes: flashing the first flash-rich CO methanol to obtain semi-lean methanol and the first CO product gas. Preferably, the pressure of the first flash is 0.05 - 0.08 MPa(G). 2 The methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C. 2 The methanol is divided into two streams. The first flash-rich CO methanol directly undergoes the first flash, and the second flash-rich CO methanol undergoes the second flash after the second cooling. Preferably, the temperature of the material after the second cooling is -55 to -50 °C.

[0058] In some embodiments of the present invention, preferably, the CO molar content in the semi-lean methanol is 20 - 24%, the H₂S molar content is ≤0.5 ppm; the temperature is -65 to -62 °C; the pressure is 0.05 - 0.08 MPa(G). 2 In some embodiments of the present invention, preferably, the CO molar content in the semi-lean methanol is 20 - 24%, the H₂S molar content is ≤0.5 ppm; the temperature is -65 to -62 °C; the pressure is 0.05 - 0.08 MPa(G). 2 the H₂S molar content is ≤0.5 ppm; the temperature is -65 to -62 °C; the pressure is 0.05 - 0.08 MPa(G).

[0059] In some embodiments of the present invention, further preferably, the semi-lean methanol is divided into the first semi-lean methanol and the second semi-lean methanol with a molar flow ratio of 3.5 - 4.5:1. In the present invention, the second semi-lean methanol is sent to the subsequent process for use.

[0060] In the present invention, the first semi-lean methanol is divided into three streams, which are respectively returned and undergo the CO absorption, the second washing, and the third washing. Preferably, the first semi-lean methanol is divided into the A-stream semi-lean methanol, the B-stream semi-lean methanol, and the C-stream semi-lean methanol with a molar flow ratio of 13 - 15:1:3 - 5. 2 In the present invention, the first semi-lean methanol is divided into three streams, which are respectively returned and undergo the CO absorption, the second washing, and the third washing. Preferably, the first semi-lean methanol is divided into the A-stream semi-lean methanol, the B-stream semi-lean methanol, and the C-stream semi-lean methanol with a molar flow ratio of 13 - 15:1:3 - 5.

[0061] In the present invention, the process of the second flash includes: flashing the material after the second cooling to obtain the second CO product gas. 2Product gas and the solution after flash evaporation. Preferably, the pressure of the second flash evaporation is 0.06 - 0.09 MPa (G).

[0062] In the present invention, the 2 process of H 2 S flash evaporation includes: subjecting the first H 2 S-rich methanol to H 2 S flash evaporation to obtain H 2 S flash evaporation gas and the H 2 S-rich methanol after flash evaporation. Preferably, the pressure of the H

[0063] S flash evaporation is 1.6 - 2 MPa (G). 2 In some embodiments of the present invention, preferably, the molar content of H 2 S in the H 2 S-rich methanol after flash evaporation is 1.2 - 1.4%, and the molar content of CO

[0064] is 35 - 40%; the temperature is -16 to -10 °C. 2 In the present invention, the third cooling is achieved by reducing the temperature of the H

[0065] S-rich methanol after flash evaporation, aiming to lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. Preferably, the temperature of the material after the third cooling is -36 to -33 °C. 2 In the present invention, the process of the third flash evaporation includes: subjecting the material after the third cooling to flash evaporation to obtain the third H

[0066] S-rich methanol 16 and sulfur-containing gas phase. Preferably, the pressure of the third flash evaporation is 0.12 - 0.16 MPa (G). 2 In some embodiments of the present invention, preferably, the molar content of H 2 S in the third H 2 S-rich methanol obtained by the third flash evaporation is 1.2 - 1.4%, and the molar content of CO 2 is 25 - 30%; the temperature is -69 to -65 °C; the pressure is 0.13 - 0.17 MPa (G). In the present invention, the third H

[0067] S-rich methanol is sent to subsequent processes for treatment. 2 In the present invention, the process of the first washing includes: washing the solution after the second flash evaporation and the sulfur-containing gas phase obtained by the third flash evaporation to obtain the third CO 2 product gas and low-H

[0068] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-H 2The molar content of S is 0.5 - 0.8%, and the molar content of CO 2 is 26 - 29%; the temperature is -65 to -60 °C, and the pressure is 0.12 - 0.16 MPa(G).

[0069] In some embodiments of the present invention, preferably, the first CO 2 product gas obtained from the first flash evaporation, the second CO 2 product gas obtained from the second flash evaporation, and the third CO 2 product gas obtained from the first washing are mixed to obtain a CO 2 product gas; more preferably, the molar content of H 2 S in the CO 2 product gas is ≤ 1 ppm, and the molar content of CO 2 is 99.4 - 99.7%; the temperature is -66 to -63 °C, and the pressure is 0.05 - 0.08 MPa(G).

[0070] In the present invention, the process of the second washing includes: washing the semi-lean methanol of the B stream and the CO 2 flash gas obtained from the CO 2 flash evaporation to obtain a first flash gas. Preferably, the temperature of the first flash gas is -58 to -54 °C, and the pressure is 1.6 - 2 MPa(G).

[0071] In the present invention, the process of the third washing includes: washing the semi-lean methanol of the C stream and the H 2 S flash gas obtained from the H 2 S flash evaporation to obtain a second flash gas and low-sulfur carbon-rich methanol. Preferably, the temperature of the second flash gas is -62 to -58 °C, and the pressure is 1.6 - 2 MPa(G).

[0072] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-sulfur carbon-rich methanol is 0.2 - 0.3%, and the molar content of CO 2 is 35 - 40%; the temperature is -20 to -15 °C.

[0073] In the present invention, preferably, the first flash gas and the second flash gas are mixed to obtain a flash gas.

[0074] The second aspect of the present invention provides a structural schematic diagram of a low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device as shown in Figure 1 shown, and it can be seen from Figure 1 that the device includes: an H 2 S absorption tower T-1, a CO 2Absorption column T-2, medium-pressure flash column T-3 and reabsorption column T-4, as well as the first cooler E-1, the second cooler E-2 and the third cooler E-3; the medium-pressure flash column T-3 includes a CO 2 flash section provided thereon and an H 2 S flash section provided therebelow, and the H 2 S flash section is divided into an upper section and a lower section;

[0075] Synthesis gas 1 enters the H 2 S absorption column T-1 for H 2 S absorption to obtain the first rich H 2 S methanol 4 and desulfurized gas 5; the desulfurized gas 5 enters the CO 2 absorption column T-2 for CO 2 absorption to obtain the rich CO 2 methanol 6 is divided into two streams. The first stream of rich CO 2 methanol 6-i is recycled to the H 2 S absorption column T-1. The second stream of rich CO 2 methanol 6-ii enters the CO 2 flash section after passing through the first cooler E-1 for CO 2 flash to obtain the flashed rich CO 2 methanol 13 is divided into two streams. The first stream of flashed rich CO 2 methanol 13-i enters the upper part of the reabsorption column T-4 for the first flash to obtain the semi-lean liquid methanol 8 which is divided into two streams. The second stream of flashed rich CO 2 methanol 13-ii enters the middle part of the reabsorption column T-4 after passing through the second cooler E-2 for the second flash;

[0076] The first rich H 2 S methanol 4 enters the lower section of the H 2 S flash section for H 2 S flash to obtain the flashed rich H 2 S methanol 14 enters the lower part of the reabsorption column T-4 after passing through the third cooler E-3 for the third flash. The obtained sulfur-containing gas phase and the flashed solution obtained from the second flash are subjected to the first washing to obtain the low H 2 S methanol 2 is recycled to the H 2 S absorption column T-1;

[0077] Among them, the first stream of semi-lean liquid methanol 8-i is divided into three streams. The A stream of semi-lean liquid methanol 8-i-A is recycled to the CO 2 absorption column T-2. The B stream of semi-lean liquid methanol 8-i-B is recycled to the CO 2 flash section for the second washing. The C stream of semi-lean liquid methanol 8-i-C is recycled to the H 2The upper part of the S flash section is subjected to a third washing, and the obtained low-sulfur carbon-rich methanol 11 is recycled and reused in the H 2 S absorption tower T-1.

[0078] In the present invention, as Figure 1 shown, the device further includes: a low-H 2 S methanol outlet connecting the reabsorption tower T-4 and a pipeline of the H 2 S absorption tower T-1 is provided with a first pump P-1 for boosting the low-H 2 S methanol 2 after the first pressurization and recycling it back to the H 2 S absorption tower T-1.

[0079] In the present invention, as Figure 1 shown, the device further includes: in the direction of material flow, connecting the rich-CO 2 methanol outlet of the CO 2 absorption tower T-2 and a pipeline of the H 2 S absorption tower T-1 are successively provided with a second pump P-2 and a fourth cooler E-4 for successively subjecting the first stream of rich-CO 2 methanol 6-i to a second pressurization and a fourth cooling and then recycling it back to the H 2 S absorption tower T-1.

[0080] In the present invention, as Figure 1 shown, the device further includes: connecting the semi-lean liquid methanol outlet of the reabsorption tower T-4, the CO 2 absorption tower T-2, the CO 2 flash section and a pipeline of the H 2 S flash section is provided with a third pump P-3 for boosting the first stream of semi-lean liquid methanol 8-i after the third pressurization and dividing it into three streams, which are respectively recycled and reused in the CO 2 absorption tower T-2, the CO 2 flash section and the H 2 S flash section.

[0081] In the present invention, as Figure 1 shown, the device further includes: connecting the low-sulfur carbon-rich methanol outlet of the H 2 S flash section and a pipeline of the H 2 S absorption tower T-1 is provided with a fourth pump P-4 for boosting the low-sulfur carbon-rich methanol 11 after the fourth pressurization and recycling it back to the H 2 S absorption tower T-1.

[0082] In the present invention, as Figure 1 shown, the H 2 S absorption tower T-1 includes a pre-washing section arranged below and a main washing section arranged above; preferably, the low-H 2The S methanol 2 is divided into two streams and recycled back to the pre-washing section and the main washing section respectively; further preferably, the first stream of rich CO 2 methanol 6-i and the low-sulfur rich-carbon methanol 11 are each independently recycled back to the main washing section.

[0083] In the present invention, as Figure 1 shown, in the H 2 S absorption tower T-1, in the pre-washing section, the first stream of low-H 2 S methanol 2-i pre-washes and absorbs H 2 S, HCN, and NH 3 in the syngas 1; in the main washing section, by introducing the second stream of low-H 2 S methanol 2-ii, the low-sulfur rich-carbon methanol 11, and the first stream of rich CO 2 methanol 6-i, H 2 S and CO 2 in the syngas after pre-washing are absorbed, realizing the recycling of the low-H 2 S methanol 2 and the low-sulfur rich-carbon methanol 11, reducing the usage amount of the first stream of rich CO 2 methanol 6-i, which is equivalent to reducing the first rich-H 2 S methanol that needs to be thermally regenerated; in addition, such a setting correspondingly reduces the working load of the subsequent CO 2 absorption tower, which is also of positive significance for reducing the usage amounts of lean methanol and semi-lean methanol in the CO 2 absorption tower.

[0084] In the present invention, as Figure 1 shown, in the H 2 S absorption tower T-1, the pre-washing section and the main washing section are connected by riser holes; the pre-washing section is connected to the low-H 2 S methanol outlet of the re-absorption tower T-4, used to contact the syngas 1 with the first stream of low-H 2 S methanol 2-i for pre-washing to obtain the second rich-H 2 S methanol 3 and the pre-washed syngas; the main washing section is connected to the low-H 2 S methanol outlet of the re-absorption tower T-4, the low-sulfur rich-carbon methanol outlet of the H 2 S flash section, and the rich CO 2 methanol outlet of the CO 2 absorption tower T-2, used to contact the pre-washed syngas with the second stream of low-H 2 S methanol 2-ii, the low-sulfur rich-carbon methanol 11, and the first stream of rich CO 2 methanol 6-i for main washing to obtain the desulfurized gas 5 and the first rich-H 2 S methanol 4.

[0085] In some embodiments of the present invention, preferably, the H 2 In the S absorption tower T-1, the number of trays in the pre-washing section is 9-12, and the number of trays in the main washing section is 60-80.

[0086] In the present invention, unless otherwise specified, the H 2 In the pre-wash section of the S absorber, the synthesis gas and the first low H 2 S methanol 2-i is preferably contacted with synthesis gas 1 and the first low H 2 S methanol 2-i countercurrent contact, that is, synthesis gas 1 enters from the bottom of the pre-washing section, the first low H 2 S methanol 2-i enters from the upper part of the pre-washing section.

[0087] In the present invention, if Figure 1 As shown, the CO 2 The absorption tower T-2 includes a pre-purification section arranged at the bottom and a main purification section arranged at the top, and the lower part of the main purification section is connected to the upper part of the pre-purification section.

[0088] In the present invention, if Figure 1 As shown, the CO 2 In the absorption tower T-2, the pre-purification section and the main purification section are connected through a gas riser, wherein the upper part of the pre-purification section is connected to the lower part of the main purification section, which is used to separate the desulfurized gas 5 from the CO 2 Methanol 7 is contacted and pre-purified to obtain the CO-rich 2 Methanol 6 and pre-purified gas; the main purification section is connected to the semi-lean liquid methanol outlet of the reabsorption tower T-4 and the lean methanol 9 from the subsequent process, which is used to contact the pre-purified gas with the A-share semi-lean liquid methanol 8-iA and lean methanol 9 in sequence and perform main purification to obtain the purified gas 10 and CO 2 Methanol 7.

[0089] In the present invention, if Figure 1 As shown in the figure, according to the material flow direction, a fifth cooler E-5 is provided on the pipeline connecting the main purification section and the pre-purification section, which is used to cool the CO 2 After the fifth cooling, methanol 7 is recycled back to the pre-purification section.

[0090] In some embodiments of the present invention, preferably, the CO 2 In the absorption tower T-2, the number of trays in the pre-purification section is 12-18, and the number of trays in the main purification section is 60-80.

[0091] In the present invention, unless otherwise specified, the CO 2 In the pre-purification section of absorption tower T-2, desulfurized gas 5 and CO 2 Methanol 7 is preferably contacted with desulfurized gas 5 and CO​​​​​2 The methanol 7 is in countercurrent contact; that is, the desulfurized gas 5 enters from the bottom of the pre-purification section, and the CO-containing 2 methanol 7 enters from the upper part of the main purification section.

[0092] In the present invention, as Figure 1 shown, in the medium-pressure flash tower T-3, a CO 2 flash section is provided for subjecting the second CO-rich 2 methanol 6-ii to CO 2 flash after the first cooling to obtain CO 2 flash gas and CO-rich 2 methanol 13 after flashing. Among them, the CO 2 flash gas and the B-share semi-lean liquid methanol 8-i-B are subjected to a second washing to obtain the first flash gas 12-i. In the present invention, unless otherwise specified, the CO-rich 2 methanol 13 after flashing also includes the washing liquid obtained from the second washing.

[0093] In the present invention, as Figure 1 shown, in the medium-pressure flash tower T-3, an H 2 S flash section is provided at the lower part. The upper and lower parts of the H 2 S flash section are connected by upflow holes; specifically, the lower part of the H 2 S flash section is used to subject the first H-rich 2 S methanol 4 to H 2 S flash to obtain H 2 S flash gas and H-rich 2 S methanol after flashing. And the H 2 S flash gas enters the upper part of the H 2 S flash section for a third washing with the C-share semi-lean liquid methanol 8-i-C to obtain the second flash gas 12-ii and low-sulfur carbon-rich methanol 11.

[0094] In the present invention, as Figure 1 shown, the upper and middle parts of the reabsorption tower T-4 are connected by upflow holes, and the middle and lower parts are also connected by upflow holes. Specifically, the upper part is used to subject the first flash gas CO-rich 2 methanol 13-i to a first flash to obtain semi-lean liquid methanol 8 and the first CO 2 product gas; the middle part is used to subject the second flash gas CO-rich 2 methanol 13-ii to a second flash after the second cooling to obtain the flashed solution and the second CO 2 product gas; the lower part is used to subject the H-rich 2 S methanol 14 after the third cooling to a third flash to obtain the third H-rich 2S methanol 16 and sulfur-containing gas phase; wherein, the sulfur-containing gas phase and the flashed solution are subjected to a first washing to obtain low H 2 S methanol 2 and the third CO 2 Product gas; CO 2 Product gas 15 includes the first CO 2 Product gas, the second CO 2 Product gas and the third CO 2 Product gas.

[0095] The present invention will be described in detail below through embodiments.

[0096] Example 1

[0097] The low-temperature and low-sulfur syngas purification device supporting the coal water slurry gasification device is as Figure 1 shown, and it can be seen from Figure 1 that this device includes: H 2 S absorption tower T-1, CO 2 absorption tower T-2, medium-pressure flash tower T-3 and reabsorption tower T-4, the first cooler E-1, the second cooler E-2, the third cooler E-3, the fourth cooler E-4 and the fifth cooler E-5, as well as the first pump P-1, the second pump P-2, the third pump P-3 and the fourth pump P-4;

[0098] H 2 S absorption tower T-1 includes a pre-washing section provided at the lower part and a main washing section provided at the upper part; CO 2 absorption tower T-2 includes a pre-purification section provided at the lower part and a main purification section provided at the upper part; the medium-pressure flash tower T-3 includes a CO 2 flash section provided at the upper part and an H 2 S flash section provided at the lower part, and the H 2 S flash section is divided into an upper section and a lower section.

[0099] The low-temperature and low-sulfur syngas purification method for the coal water slurry gasification device supporting it, this method includes:

[0100] Mixing syngas 1 (the molar content of H 2 S is 0.9-1.2%, the molar content of CO 2 is 40-50%; the temperature is -15 to -5 °C, and the pressure is 5.2-5.7 MPa (G)) and the first low-H 2 S methanol 2-i are in counter-current contact at a molar flow ratio of 70-80:1 and subjected to pre-purification to obtain the second H-rich 2 S methanol 3 (the molar content of H 2 S is 0.2-0.4%, the molar content of CO 2 is 70-75%) and the pre-washed syngas;

[0101] The pre-washed synthesis gas is mixed with the second low H 2 S methanol 2-ii, low sulfur carbon-rich methanol 11 (pressurized to 5.6-6MPa(G) after the fourth boost) and the first CO-rich 2 Methanol 6-i (after the second pressurization to 5.6-6MPa (G) and the fourth cooling to -35 to -25°C) is countercurrently contacted and subjected to main washing to obtain desulfurized gas 5 (H 2 The molar content of S is 0.5-1ppm, CO 2 The molar content of is 36-40%; the temperature is -20 to -10°C; the pressure is 5.3-5.4MPa(G)) and the first H-rich 2 S methanol 4 (H 2 The molar content of S is 1.2-1.4%, CO 2 The molar content of is 38-42%; the temperature is -20 to -10°C, and the pressure is 5.3-5.4MPa(G));

[0102] Among them, the low H 2 S methanol 2 is first pressurized to 5.6-6MPa(G) and then divided into the first stream of low H with a molar flow ratio of 1:11-13 2 S methanol 2-i and second strand low H 2 S methanol 2-ii; Synthesis gas 1 and second low H 2 The molar flow ratio of S methanol 2-ii is 5-6:1; the molar flow ratio of synthesis gas 1 and low sulfur carbon-rich methanol 11 is 7-8:1; the molar flow ratio of synthesis gas 1 and the first CO-rich 2 The molar flow ratio of methanol 6-i is 2-3:1;

[0103] The above desulfurized gas 5 and CO 2 Methanol 7 (fifth cooling to -36 to -34°C) is countercurrently contacted and pre-purified at a molar flow ratio of 1:1.1-1.4 to obtain CO-rich 2 Methanol 6(CO 2 The molar content of is 30-34%, H 2 The molar content of S is 0.1-0.5ppm; the temperature is -15 to -10℃, the pressure is 5.2-5.4MPa(G)) and pre-purified gas, wherein the CO-rich 2 Methanol 6 is divided into the first stream rich in CO with a molar flow ratio of 1:2-2.3 2 Methanol 6-i and the second CO-rich stream 2 Methanol 6-ii;

[0104] The above pre-purified gas is mixed with A-stream semi-lean methanol 8-iA, lean methanol 9(CO 2 The molar content of is 0%, H 2 ​​​Contact countercurrently with a molar content of S of 0%) and perform primary purification to obtain purified gas 10 (H 2 The molar content of S ≤ 0.1 ppm, CO 2 The molar content of ≤ 20 ppm; the temperature is -55 to -50 °C; the pressure is 5.2 - 5.3 MPa (G)) and containing CO 2 methanol 7;

[0105] Among them, the molar flow ratio of the above-mentioned purified gas 10 and A-share semi-lean liquid methanol 8-i-A is 1.4 - 1.6:1; the molar flow ratio of the above-mentioned purified gas 10 and lean methanol 9 is 1:1.1 - 1.2;

[0106] Cool the second rich CO 2 methanol 6-ii to -36 to -34 °C for the first time, and then perform CO 2 flash evaporation (pressure is 1.6 - 2 MPa (G)) to obtain rich CO after flash evaporation 2 methanol 13 (H 2 The molar content of S is 0.1 - 0.5 ppm, CO 2 The molar content of is 29 - 33%; the temperature is 38 to -35 °C) and CO 2 flash gas; the first rich H 2 S methanol 4 is subjected to H 2 S flash evaporation (pressure is 1.6 - 2 MPa (G)) to obtain rich H after flash evaporation 2 S methanol 14 (H 2 The molar content of S is 1.2 - 1.4%, CO 2 The molar content of is 35 - 40%; the temperature is -16 to -10 °C) and H 2 S flash gas;

[0107] The rich CO after the above flash evaporation 2 Methanol 13 is divided into the first rich CO after flash evaporation with a molar flow ratio of 3 - 3.6:1 2 Methanol 13-i and the second rich CO after flash evaporation 2 Methanol 13-ii, among which, the first rich CO after flash evaporation 2 Methanol 13-i is subjected to the first flash evaporation (pressure is 0.05 - 0.08 MPa (G)) to obtain the first CO 2 Product gas and semi-lean liquid methanol 8 (CO 2 The molar content of is 20 - 24%, H 2 The molar content of S ≤ 0.5 ppm; the temperature is -65 to -62 °C; the pressure is 0.05 - 0.08 MPa (G)), the second rich CO after flash evaporation 2After the methanol 13-ii is secondarily cooled to -55 to -50 °C, a second flash evaporation is carried out (at a pressure of 0.06 - 0.09 MPa(G)) to obtain a second CO 2 product gas and the solution after flash evaporation; the rich H 2 S methanol 14 is tertially cooled to -36 to -33 °C and then undergoes a third flash evaporation (at a pressure of 0.12 - 0.16 MPa(G)) to obtain a sulfur-containing gas phase and a third rich H 2 S methanol 16 (the molar content of H 2 S is 1.2 - 1.4%, and the molar content of CO 2 is 25 - 30%; the temperature is -69 to -65 °C; the pressure is 0.13 - 0.17 MPa(G)); the above sulfur-containing gas phase and the solution after flash evaporation are subjected to a first washing to obtain a third CO 2 product gas and low-H 2 S methanol 2 (the molar content of H 2 S is 0.5 - 0.8%, and the molar content of CO 2 is 26 - 29%; the temperature is -65 to -60 °C, and the pressure is 0.12 - 0.16 MPa(G));

[0108] Among them, the above first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas are mixed to obtain a CO 2 product gas 15 (the molar content of H 2 S ≤ 1 ppm, and the molar content of CO 2 is 99.4 - 99.7%; the temperature is -66 °C to -63 °C, and the pressure is 0.05 - 0.08 MPa(G));

[0109] Among them, the above semi-lean liquid methanol 8 is divided into a first semi-lean liquid methanol 8-i and a second semi-lean liquid methanol 8-ii with a molar flow rate ratio of 3.5 - 4.5:1; and the above first semi-lean liquid methanol 8-i is tertially pressurized to 5.6 - 5.8 MPa(G) and then divided into an A-share semi-lean liquid methanol 8-i-A, a B-share semi-lean liquid methanol 8-i-B, and a C-share semi-lean liquid methanol 8-i-C with a molar flow rate ratio of 13 - 15:1:3 - 5; among them, the A-share semi-lean liquid methanol 8-i-A is returned for main washing; the B-share semi-lean liquid methanol 8-i-B and the above CO 2 flash gas are subjected to a second washing to obtain a first flash gas 12-i (the temperature is -58 °C to -54 °C, and the pressure is 1.6 - 2 MPa(G)); the C-share semi-lean liquid methanol 8-i-C and the H 2 S flash gas are subjected to a third washing to obtain a second flash gas 12-ii (the temperature is -62 °C to -58 °C, the pressure is 1.6 - 2 MPa(G)) and low-sulfur carbon-rich methanol 11 (H2 The molar content of S is 0.2 - 0.3%, and the molar content of CO 2 is 35 - 40%; the temperature is -20 to -15 °C); after the above-mentioned low-sulfur and carbon-rich methanol 11 is pressurized to 5.6 - 6 MPa(G) for the fourth time, it is returned and subjected to main washing.

[0110] Comparative Example 1

[0111] Taking the hydrogen production device using coal water slurry gasification as an example, the effective gas (H 2 +CO) entering the low-temperature methanol washing device is 230,000 Nm 3 / h. Based on this benchmark, the main technical parameters of the lean liquid - semi-lean liquid process (that is, CN201110260570.0 discloses a low-temperature methanol washing process) are compared in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] It can be seen from the results in Table 1 that taking the hydrogen production device based on coal water slurry gasification as an example, for the low-temperature and low-sulfur syngas purification method of the supporting coal water slurry gasification device provided in Example 1, the lean methanol circulation volume is 91.8% of the lean methanol circulation volume in Comparative Example 1 (lean liquid - semi-lean liquid process), and the semi-lean liquid methanol circulation volume is 90.7% of the semi-lean liquid methanol circulation volume in Comparative Example 1 (lean liquid - semi-lean liquid process). The consumption of rich CO 2 in the H 2 S absorption tower is 75.8% of the rich CO 2 methanol consumption in Comparative Example 1 (lean liquid - semi-lean liquid process), and the cumulative reduction of external cold consumption is 700 KW / h, with a significant overall energy-saving effect.

[0116] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for purifying low-temperature, low-sulfur syngas from a coal-water slurry gasification device, characterized in that: The method comprises: The synthesis gas is subjected to H2S absorption to obtain a first H2S-rich methanol and a desulfurized gas; the desulfurized gas is subjected to CO2 absorption to obtain a CO2-rich methanol, and the obtained CO2-rich methanol is divided into two streams; the second CO2-rich methanol is subjected to CO2 flash distillation after a first cooling to obtain a flashed CO2-rich methanol, and the obtained flashed CO2-rich methanol is divided into two streams; the first flashed CO2-rich methanol is subjected to a first flash distillation to obtain a semi-lean liquid methanol, and the second flashed CO2-rich methanol is subjected to a second flash distillation after a second cooling; the first H2S-rich methanol is subjected to H2S flash distillation to obtain a flashed H2S-rich methanol, and the obtained flashed H2S-rich methanol is subjected to a third flash distillation after a third cooling, and the obtained sulfur-containing gas phase and the flashed solution obtained by the second flash distillation are subjected to a first washing to obtain low-H2S methanol; The first stream of semi-lean methanol is divided into three streams, stream A of the semi-lean methanol is returned and subjected to the CO2 absorption, stream B of the semi-lean methanol is subjected to a second washing with the CO2 flash gas obtained by flash distillation of CO2, and stream C of the semi-lean methanol is subjected to a third washing with the H2S flash gas obtained by flash distillation of H2S to obtain low-sulfur and carbon-rich methanol; the low-H2S methanol, the first stream of CO2-rich methanol and the low-sulfur and carbon-rich methanol are each independently returned and subjected to the H2S absorption.

2. The method according to claim 1, wherein: After the low H2S methanol is first pressurized to 5.6-6 MPa(G), it is returned and subjected to the H2S absorption; And / or, according to the material flow direction, the first stream of CO2-rich methanol is successively pressurized to 5.6-6 MPa (G) and cooled to -35 to -25°C, and then returned to perform the H2S absorption; and / or, the first stream of semi-lean methanol is pressurized to 5.6-5.8 MPa(G) for a third time, and then divided into the A stream of semi-lean methanol, the B stream of semi-lean methanol and the C stream of semi-lean methanol; And / or, the low-sulfur and carbon-rich methanol is pressurized to 5.6-6 MPa(G) for the fourth time and then returned to perform the H2S absorption.

3. The method according to claim 1 or 2, wherein: The H2S absorption process comprises: contacting the synthesis gas with a first stream of low H2S methanol and performing pre-washing to obtain a second H2S-rich methanol and a pre-washed synthesis gas; contacting the pre-washed synthesis gas with a second stream of low H2S methanol, a low-sulfur carbon-rich methanol and a first stream of CO2-rich methanol in sequence and performing main washing to obtain the first H2S-rich methanol and desulfurized gas; wherein the low H2S methanol is divided into the first stream of low H2S methanol and the second stream of low H2S methanol at a molar flow ratio of 1:13-15; and / or, the molar content of H2S in the synthesis gas is 0.9-1.2%, the molar content of CO2 is 40-50%; the temperature is -15 to -5°C, and the pressure is 5.2-5.7MPa(G); and / or, the molar content of H2S in the first H2S-rich methanol is 1.2-1.4%, the molar content of CO2 is 38-42%; the temperature is -20 to -10°C, and the pressure is 5.3-5.4 MPa(G); And / or, the molar content of H2S in the desulfurized gas is 0.5-1 ppm, the molar content of CO2 is 36-40%; the temperature is -20 to -10°C; and the pressure is 5.3-5.4 MPa(G).

4. The method according to any one of claims 1 to 3, wherein: The CO2-rich methanol is divided into a first stream of CO2-rich methanol and a second stream of CO2-rich methanol with a molar flow ratio of 1:2-2.3; And / or, the CO2 absorption process includes: contacting the desulfurized gas with CO2-containing methanol and pre-purifying it to obtain pre-purified gas and the CO2-rich methanol; contacting the pre-purified gas with A-share semi-lean liquid methanol and lean methanol in sequence and performing main purification to obtain the CO2-containing methanol and purified gas; and / or, the molar content of CO2 in the CO2-rich methanol is 30-34%, the molar content of H2S is 0.1-0.5 ppm; the temperature is -15 to -10°C, and the pressure is 5.2-5.4 MPa(G); Preferably, the CO2-containing methanol is cooled to -36 to -34°C for the fifth time and then returned to perform the pre-absorption.

5. The method according to any one of claims 1 to 4, wherein: The temperature of the material after the first cooling is -36 to -34°C; And / or, the pressure of the CO2 flash evaporation is 1.6-2MPa(G); and / or, dividing the flashed CO2-rich methanol into the first stream of flashed CO2-rich methanol and the second stream of flashed CO2-rich methanol at a molar flow ratio of 3-3.6:1; and / or, the molar content of H2S in the CO2-rich methanol after the flash evaporation is 0.1-0.5 ppm, and the molar content of CO2 is 29-33%; the temperature is -38 to -35°C; And / or, the pressure of the H2S flash evaporation is 1.6-2MPa(G); And / or, the molar content of H2S in the H2S-rich methanol after the flash evaporation is 1.2-1.4%, and the molar content of CO2 is 35-40%; the temperature is -16 to -10°C.

6. The method according to any one of claims 1 to 5, wherein: The temperature of the material after the second cooling is -55 to -50°C; And / or, the pressure of the first flash evaporation is 0.05-0.08 MPa(G); and / or, the molar content of CO2 in the semi-lean methanol is 20-24%, the molar content of H2S is ≤0.5ppm; the temperature is -65 to -62°C; the pressure is 0.05-0.08MPa(G); and / or, dividing the semi-lean methanol into the first stream of semi-lean methanol and the second stream of semi-lean methanol at a molar flow ratio of 3.5-4.5:1; and / or, dividing the first stream of semi-lean methanol into the A stream of semi-lean methanol, the B stream of semi-lean methanol and the C stream of semi-lean methanol at a molar flow ratio of 13-15:1:3-5; And / or, the pressure of the second flash evaporation is 0.06-0.09 MPa(G); and / or, the molar content of H2S in the low H2S methanol is 0.5-0.8%, the molar content of CO2 is 26-29%; the temperature is -65 to -60°C, and the pressure is 0.12-0.16MPa(G); And / or, the temperature of the material after the third cooling is -36 to -33°C; And / or, the pressure of the third flash evaporation is 0.12-0.16 MPa(G); and / or, mixing the first CO2 product gas obtained by the first flash evaporation, the second CO2 product gas obtained by the second flash evaporation, and the third CO2 product gas obtained by the first washing to obtain the CO2 product gas; Preferably, the molar content of H2S in the CO2 product gas is ≤1ppm, the molar content of CO2 is 99.4-99.7%; the temperature is -66 to -63°C, and the pressure is 0.05-0.08MPa(G).

7. The method according to any one of claims 1 to 6, wherein: The molar content of H2S in the low-sulfur and carbon-rich methanol is 0.2-0.3%, and the molar content of CO2 is 35-40%; the temperature is -20 to -15°C; and / or, the temperature of the first flash gas obtained by the second washing is -58 to -54°C and the pressure is 1.6 to 2 MPa(G); and / or, the temperature of the second flash gas obtained by the third washing is -62 to -58°C and the pressure is 1.6 to 2 MPa(G); Preferably, the first flash gas and the second flash gas are mixed to obtain the flash gas.

8. A low-temperature, low-sulfur synthesis gas purification device supporting a water-coal slurry gasification device, characterized in that: The device comprises: an H2S absorption tower, a CO2 absorption tower, a medium-pressure flash tower and a reabsorption tower connected in sequence, as well as a first cooler, a second cooler and a third cooler; the medium-pressure flash tower comprises a CO2 flash section arranged on the top and an H2S flash section arranged on the bottom, and the H2S flash section is divided into an upper section and a lower section; The synthesis gas enters the H2S absorption tower for H2S absorption to obtain the first H2S-rich methanol and the desulfurized gas; the desulfurized gas enters the CO2 absorption tower for CO2 absorption, and the obtained CO2-rich methanol is divided into two streams, the first stream of CO2-rich methanol is recycled back to the H2S absorption tower, the second stream of CO2-rich methanol passes through the first cooler, enters the CO2 flash section for CO2 flash evaporation, and the obtained flashed CO2-rich methanol is divided into two streams, the first stream of CO2-rich methanol after flash evaporation enters the upper part of the reabsorption tower for the first flash evaporation, and the obtained semi-lean liquid methanol is divided into two streams, the second stream of CO2-rich methanol after flash evaporation passes through the second cooler, and enters the middle part of the reabsorption tower for the second flash evaporation; The first H2S-rich methanol enters the lower section of the H2S flash section for H2S flash evaporation, the flashed H2S-rich methanol obtained passes through the third cooler, and then enters the lower part of the reabsorption tower for the third flash evaporation, the obtained sulfur-containing gas phase and the flashed solution obtained by the second flash evaporation are first washed, and the obtained low-H2S methanol is recycled to the H2S absorption tower; Among them, the first stream of semi-lean methanol is divided into three streams, stream A of semi-lean methanol is recycled back to the CO2 absorption tower, stream B of semi-lean methanol is recycled back to the CO2 flash section for the second washing, stream C of semi-lean methanol is recycled back to the upper section of the H2S flash section for the third washing, and the obtained low-sulfur and carbon-rich methanol is recycled back to the H2S absorption tower.

9. The device according to claim 8, wherein: The device further comprises: a first pump is arranged on a pipeline connecting the low H2S methanol outlet of the reabsorption tower and the H2S absorption tower; And / or, the device further comprises: a second pump and a fourth cooler are sequentially arranged on the pipeline connecting the CO2-rich methanol outlet of the CO2 absorption tower and the H2S absorption tower according to the material flow direction; And / or, the device further comprises: a third pump is provided on the pipeline connecting the semi-lean liquid methanol outlet of the reabsorption tower, the CO2 absorption tower, the CO2 flash section and the H2S flash section, for dividing the first stream of semi-lean liquid methanol into three streams after the third boosting; And / or, the device further comprises: a fourth pump is arranged on the pipeline connecting the low-sulfur and carbon-rich methanol outlet of the H2S flash section and the H2S absorption tower.

10. The device according to claim 8 or 9, wherein: The H2S absorption tower comprises a pre-washing section arranged at the bottom and a main washing section arranged at the top; Preferably, the low H2S methanol is divided into two streams and recycled back to the pre-washing section and the main washing section respectively; Preferably, the first stream of CO2-rich methanol and low-sulfur carbon-rich methanol are independently recycled back to the main washing section; And / or, the CO2 absorption tower comprises a pre-purification section arranged at the bottom and a main purification section arranged at the top, and the lower part of the main purification section is connected to the upper part of the pre-purification section; Preferably, a fifth cooler is provided on the pipeline connecting the main purification section and the pre-purification section according to the material flow direction.

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